For the past 50 years, researchers have searched in vain for gravitational waves: miniscule ripples in space-time emitted from the most violent events in the cosmos. To move gravitational-wave detection beyond the realm of impossibility, we have just finished construction on Advanced LIGO, a pair of 4 km arm length laser interferometers capable of measuring displacements approaching 10-19 m at their most sensitive frequencies, redefining the meaning of "extreme precision measurement". LIGO brings together high energy astrophysics and many aspects of optical science and engineering in a unique way with the ambitious goal of detecting gravitational waves and opening a new window onto the universe.